Conventional dielectric thin film material used in the semiconductor industry comprises silicon dioxide (SiO.sub.2). However, future electronic memory technology will demand thin film materials exhibiting a greater dielectric constant than that of silicon dioxide. That is, thin films having greater dielectric constant values will permit smaller individual storage device sizes and increased memory densities on integrated memory devices.
Polycrystalline ferroelectric materials are being considered for high dielectric constant thin film materials. However, ferroelectric thin film materials tend to have exceptional properties along one crystallographic direction or axis and only moderate properties along the other crystal directions or axes. Since polycrystalline ferroelectric thin films considered to-date are comprised of randomly oriented grains, the measured dielectric constant of these films will be an average of the dielectric constants in all directions. Thus, the average dielectric constant of polycrystalline ferroelectric thin films will be considerably less than the dielectric constant exhibited along the optimum crystal direction or axis of the crystal lattice.
Strontium barium niobate (Sr.sub.x Ba.sub.1-x Nb.sub.2 O.sub.6) where x is greater than 0.25 and less than 0.75 (hereafter SBN) is a ferroelectric material exhibiting excellent dielectric and electro-optic properties which are highest along the c-axis of the tetragonal tungsten bronze crystal lattice as described by Prokhorov et al. in Ferroelectric
Crystals for Laser Radiation Control, (Adam Hilger, New York, 1990) p. 81. Initial studies of Sr.sub.x Ba.sub.1-x Nb.sub.2 O.sub.6 were carried out on Czochralski-grown single crystals as described by Neurgaonkar et al. in Ferroelectrics 15, 31 (1984). In addition, liquid-phase epitaxy, rf sputtering, and sol-gel growth of textured Sr.sub.x Ba.sub.1-x Nb.sub.2 O.sub.6 thin films have been reported. For example, liquid-phase epitaxy was used by Neurgaonkar et al. in Mater. Res. Bull. 22, 1095 (1987). Rf sputtering was used by Antisigin et al. in Ferroelectrics 63, 235 (1985), while sol-gel was employed by Xu et al. in J. Mater. Res. 5, 916 (1990) and by Hirano et al. in J. Am. Ceram. Soc. 75, 1697 (1992). Recently, growth of these films by conventional and single source metalorganic chemical vapor deposition (MOCVD) was reported by Greewald et al. in Mater. Res. Soc. Symp. Proc. 243, 457 (1993) and by Lu et al. in Mater. Res. Soc. Symp. Proc. 335, 59 (1994).
Potassium niobate (KNbO.sub.3) is promising ferroelectric material for electro-optic (EO), nonlinear optic (NLO) and photorefractive applications. The electro-optic figure of merit is 13 picometers/volt which surpasses that of LiNbO.sub.3. In addition, potassium niobate possesses excellent non-linear optical coefficients (d.sub.31 =15 picometer/volt and d.sub.33 =27 picometer/volts). The growth of KNbO.sub.3 films also has been demonstrated by liquid phase epitaxy, sol-gel, ion beam sputtering, RF sputtering and pulsed laser deposition techniques and recently by single source metal-organic chemical vapor deposition that produced polycrystalline films with a preferred orientation. However, for practical NLO and EO applications, highly textured or epitaxial thin films are required.
An object of the present invention is to provide a highly textured or epitaxial niobate ferroelectric thin film deposited on an amorphous or crystalline substrate surface with a crystal axis exhibiting a desireable property preferentially oriented or aligned relative to the substrate surface.
Another object of the present invention is to provide a MOCVD method of depositing a highly textured or oriented strontium barium or other niobate ferroelectric thin film on an amorphous as well as crystalline substrate surface with a crystal axis exhibiting a desireable property preferentially oriented or aligned to the substrate surface.
Still another object of the present invention to provide a MOCVD method of depositing a highly textured or epitaxial potassium niobate ferroelectric thin film on a substrate surface using improved precursors with a crystal axis exhibiting a desireable property preferentially oriented or aligned to the substrate surface.